Antibody-drug conjugates (ADCs) combine the binding specificity of monoclonal antibodies with the potency of chemotherapeutic agents. The technology associated with the development of monoclonal antibodies to tumor associated target molecules, the use of more effective cytotoxic agents, and the design of chemical linkers to covalently bind these components, has progressed rapidly in recent years (Ducry L., et al. Bioconjugate Chemistry, 21:5-13, 2010).
Promising ADCs such as SGN-75 (US2009/148942) and trastuzumab-DM1 (US2009/0226465) are currently in clinical trials. However, as other tumor associated antigens are considered for targets, numerous challenges remain. Each monoclonal antibody must be characterized separately, an appropriate linker designed, and a suitable cytotoxic agent identified that retains its potency upon delivery to tumor cells. One must consider the antigen density on the cancer target and whether normal tissues express the target antigen. Other considerations include whether the entire ADC is internalized upon binding the target; whether a cytostatic or cytotoxic drug is preferable when considering possible normal tissue exposure and/or the type and stage of the cancer being treated; and, whether the linker connecting the antibody to the drug payload is a cleavable or a non-cleavable linkage. Furthermore, the antibody to drug moiety conjugation ratio must be sufficient without compromising the binding activity of the antibody and/or the potency of the drug. It is evident that ADCs are complex biologics and the challenges to develop an effective ADC remain significant.
The human 5T4 tumor associated antigen is the target antigen of the present invention. It has recently been shown that the 5T4 antigen is expressed in high levels on certain highly tumorigenic cells, also called tumor-initiating cells (WO2010/111659). Tumor-initiating cells show resistance to standard therapies and are believed to be responsible for tumor recurrence and metastasis and therefore present yet another obstacle for ADC development.
The novel anti-5T4 ADCs of the present invention overcome the challenges associated with ADC technology and provide highly specific and potent ADCs that bind to tumor cells expressing the 5T4 antigen and deliver sufficient cytotoxic drug to the cells, thus providing an innovative and effective treatment for cancer.